The present disclosure describes an apparatus and process for sterilization of items, most notably surgical instruments, used in medical, dental, veterinary, or other patient-care markets. The invention relates, more particularly to an improved high velocity dry heat sterilization device to prohibit the introduction of microbial contaminants to the sterilization chamber during the entire sterilization cycle and to ensure such items once sterilized, remain sterile when removed from the high velocity dry heat sterilization device.
There are three distinct types of dry heat sterilizers: (1) Static hot air sterilizers in which air convection is generated solely by gravity as hot air rises and cooler air descends; (2) Mechanical convection sterilizers in which air is moved by blowers to uniformly distribute the heated air and equally transfer heat throughout the load; and (3) High velocity hot air sterilizers in which air is moved at a high rate, such as at 2500 feet per minute, with the flowing air serving as the heat transfer medium. Both static air and mechanical convection sterilizers require minimally one hour (at 340° F.) or two hours (at 320° F.) to achieve sterilization whereas the high velocity hot air sterilizer can sterilize in six to twelve minutes (at 375° F.), depending on instrument type or packaging.
A high velocity hot air sterilization device has been disclosed by Cox et al. in U.S. Pat. Nos. 4,824,644; 4,894,207; 4,923,681; and 4,975,245. This device was designed and marketed for use in the dental and orthodontic markets to rapidly sterilize small instruments without instrument corrosion. The Cox High Velocity Hot Air Sterilization Device accommodates wrapped or unwrapped instruments which are placed into a wire mesh, open basket and held for pre-designated times at 375° F. as prescribed under the U.S. Food and Drug Administration 510(k) notification (K8726643A and K881371). Upon completion of the sterilization cycle, the basket containing the instruments is removed from the sterilizer. In this system described by Cox et al., unwrapped instruments are subjected to potential microbial contamination from environmental sources during the sterilization process and upon removal from the sterilizer since the sterilizer allows outside air to circulate within the sterilization chamber during the sterilization cycle and because the trays are subjected to outside air following removal from the sterilizer. For dental procedures this practice is acceptable since sterilization of dental instruments has placed emphasis on obtaining complete kill of microorganisms originating from previous patients with no concern regarding contamination from microbial contaminants having environmental origin. Other high velocity hot air sterilization devices by Allen and Sildve (U.S. Pat. No. 4,935,604) and Goldman (U.S. Pat. No. 6,039,926) also operate in a similar fashion that allows unwrapped instruments to be subjected to environmental microbial contaminants.
Existing high velocity hot air sterilization devices do not address the introduction of environmental microbial contaminants during the sterilization process or afterward as detrimental to dental patient care. Most orthodontic and dental procedures are topical and are performed in an oral environment already containing high microbial concentrations and contaminants of environmental origin play no role in disease transmission from instruments. All high velocity hot air sterilization devices directly allow outside air into the air handling system by means of fans, louvered vents, or unclosed or unsealed plenums before, during, and after the sterilization cycle. In these systems any instrument or device that is not wrapped, packaged, or pouched is subjected to microbial contamination from continually introduced outside air during the sterilization cycle that has not received the prescribed time and temperature requirements necessary to ensure microbial inactivation. Upon completion of the sterilization cycle, unwrapped instruments are directly subjected to potential environmental microbial contaminants upon the opening of the sterilization chamber and their removal. No unwrapped instrument protection is afforded with existing high velocity, hot air sterilization devices.
For use in critical-care environments including dental surgical, hospital surgical, ambulatory or outpatient surgical, and veterinary surgical procedures, patient contact items must be devoid of all viable microbial contaminants to avoid infection or disease transmission. No microbial contaminants can be introduced during the sterilization process, nor can they be introduced after the sterilization process. For unwrapped or directly exposed instruments, any air introduced to the sterilization chamber after the initiation of the sterilization cycle must be subjected to the identical sterilization parameters of designated time and temperature as the instruments being sterilized. This requirement precludes the introduction of any outside air to the air handling system and hence the sterilization chamber, once the sterilization cycle has been initiated; this requirement is not followed by the prior art high velocity hot air sterilizers.
High velocity, hot air sterilization technology has the potential to meet the sterilization requirements of the critical-care medical environment as a standard sterilization technology for heat-resistant instruments or devices. However, the original design of high velocity hot air sterilizers has also limited its usefulness due to the sterilizer's inability to accommodate closed instrument containers that could assure internal sterilization parameters are achieved within an instrument container for instrument sterilization and yet maintain the sterility of those instruments from environmental microbial contamination once the instrument container was removed from the sterilizer chamber.
Although wrapping instruments had been a primary mechanism of maintaining instrument sterilization using wet steam heat, static dry heat, high velocity hot air, radiation, and chemical agents in the past, emphasis has shifted to the use of closed containers for sterilizing larger quantities of instruments and providing subsequent protection from environmental microbial contaminants. With the increased use of closed container systems in critical-care medical environments, the use of closed containers in dental practices has also become the preferred way to protect and store sterilized dental instruments.
Closed containers allowing migration of the sterilizing agent into the container for instrument sterilization have been developed to accommodate specific sterilizing agents. The design of the container and/or its portal design must be congruent with the attributes of the sterilizing agent and must not interfere with the influx of the sterilizing agent. Accordingly the container design must assure the protection of the sterilized instruments from microbial agent contamination from the point of the container's removal from the sterilizer until the container is opened for instrument use within the sterile field.
Closed containers have been designed to incorporate top and bottom perforations protected by a microbial filtering material permeable to gas or vapor sterilants, but impermeable to microorganisms. These perforations may be static, remaining continuously open and filtered. An example of such a container is described in U.S. Pat. No. 4,551,311 issued Nov. 5, 1985 to Lorenz and entitled “Sterilizer Container.”
Another design incorporates open side vents (U.S. Patent Application Publication No.: US 2003/0211023 A1; Su-Syin Wu and Charles Howlett; “Instrument Sterilization Container Having Improved Diffusion”) to allow gas or vapor sterilants into the container. Protection from microbial contaminants is accomplished through the incorporation of internal or external microbial filters by wrapping the instruments or wrapping the entire container.
The container may also be of a non-static design, providing an automatic opening and shutting mechanism. For steam sterilization the pressure differential between the inside and outside of the container triggers an automatic opening and closing of a pressure-sensitive valve (U.S. Pat. No. 5,352,416 issued Oct. 4, 1994 to Wagner and entitled “Valve Arrangement for a Sterilization Container”).
High velocity hot air sterilizers employ rapidly flowing hot air over the surface of an article to affect microbial kill. Hot air influx into the container at a sufficient rate is therefore necessitated to achieve sterilization in the prescribed time-temperature profile. Any barrier to that necessitated rate of airflow will significantly impact sterilization conditions. Research has demonstrated that container perforation coupled with fabric filtration will disturb the high velocity influx of hot air into the instrument container and have significant impact on the conditions necessary to achieve reliable instrument sterilization. Sterilization conditions cannot be achieved within an instrument container employing high velocity hot air as the sterilant when using air filtration devices designed to prevent the influx of microbial contaminants. Existing instrument containers that employ perforations in the top, sides, and/or bottom of the container also require fabric filtration to mitigate microbial contaminants and thus, prohibit the necessary conditions required for instrument sterilization by high velocity hot air. Existing instrument containers that utilize pressure valves were specifically designed for pressurized wet steam sterilizers and do not function under the non-pressurized treatment conditions employed in high velocity dry heat sterilization. Static, open vent designs still require instrument or container wrapping.
A need exists in the art for a high velocity hot air sterilizer that provides and maintains sterile conditions within the high velocity hot air sterilizer's air handling system and sterilization chamber during the complete sterilization cycle. A need also exists in the art for a high velocity hot air sterilizer that provides the capability to sterilize medical instruments within an instrument container that allows re-distribution of sterile air during the sterilization cycle, yet can be closed and sealed before removal from the high velocity hot air sterilizer upon the completion of the sterilization cycle to assure instrument sterility to point of use.